1. Field of Invention
This invention relates to systems and methods for obtaining a spatial color profile.
2. Description of Related Art
In conventional marking devices, quality defects appear in a marked image due to various factors. For example, changes in the optical density introduced by differences in laser/LED bar intensities, subsystem non-uniformities, donor roll reload, and the like can lead to image quality defects. Additionally, spatial non-uniformity errors, e.g., a situation in which pixels in one part of an image that have been defined as a certain color appear different from pixels in another part of the image that have been defined as the same color, are also present. Wire history, wire contamination, charging subsystem variations and photoreceptor variations are among the root causes for spatial non-uniformity errors in images.
Spatial non-uniformity errors can be addressed by modifying hardware or hardware operations. For example, in LED bars, exposure variations can be minimized by measuring the output of the LED elements and adjusting their duty cycle and/or intensity to ensure that all the elements have the same output. In laser exposure systems, similar duty cycle adjustments can be performed to minimize the exposure-related non-uniformities. Furthermore, routine cleaning of wires to remove contamination helps to reduce wire history-related non-uniformities.
Another known problem is the slow change in non-uniformity caused by subsystem drift and wire history effects. An example is shown in FIG. 1 for lightness measurements (L*) of a black patch uniformly developed along the process fast scan direction (x-direction) for a period of seven days. The non-uniformity curves, also known as “smiles” (or “frowns” when inverted), are labeled 11-17, respectively for the respective days. Thus, FIG. 1 shows that not only is there non-uniformity in the lightness across the fast scan direction, but this non-uniformity as a whole changes from day to day.